Method of manufacturing copper tubes by means of hydrostatic extrusion and press equipment for carrying out the method

ABSTRACT

In the manufacture of copper tubes by hydrostatic extrusion, a tubular billet is inserted in an extrusion press and extruded through a gap between a die and a mandrel to form a tube having the desired cross-section by hydrostatic pressure. The tube which is formed is led to a cooling zone at such a distance from the extrusion press that the time between shaping and cooling exceeds the recrystallization time required for annealing copper. The extruded tube is surrounded by an inert gas within a conductor tube during the passage from the press to the cooling zone.

United States Patent Stromblad et a1. Nov. 27, 1973 [54] METHOD OF MANUFACTURING COPPER 1,739,620 12/1929 Summey 72/257 TUBES BY MEANS OF HYDROSTATIC 2 25%; 5/1325 wrphy mstrom EXTRUSION AND PRESS EQUIPMENT FOR 3,585,833 6/1971 Carraher 72/257 CARRYING OUT THE METHOD Inventors: lngemar Striimblad; Rolf Hogland,

both of Vasteras, Sweden Assignee: Allmanna Svenska Elektriska Aktiebolaget, Vasteras, Sweden Filed: July 10, 1972 Appl. No.: 270,438

Foreign Application Priority Data July 27, 1971 Sweden ..9605/71 US. Cl 72/60, 72/257, 148/115 R Int. Cl. B21c 31/00 Field of Search 72/60, 257;

References Cited UNITED STATES PATENTS 11/1972 Larker 72/60 Primary ExaminerRichard J. Herbst Att0rneyJennings Bailey, Jr.

[57] ABSTRACT In the manufacture of copper tubes by hydrostatic extrusion, a tubular billet is inserted in an extrusion press and extruded through a gap between a die and a mandrel to form a tube having the desired crosssection by hydrostatic pressure. The tube which is formed is led to a cooling zone at such a distance from the extrusion press that the time between shaping and cooling exceeds the recrystallization time required for annealing copper. The extruded tube is surrounded by an inert gas within a conductor tube during the passage from the press to the cooling zone.

8 Claims, 7 Drawing Figures METHOD OF MANUFACTURING COPPER TUBES BY MEANS OF HYDROSTATIC EXTRUSION AND PRESS EQUIPMENT FOR CARRYING OUT THE METHOD BACKGROUND OF THE INVENTION Field o t e lnxsntio The present invention relates to a method of manufacturing soft copper tubes by means of hydrostatic extrusion and extrusion equipment for carrying out the method.

2. The Prior Art In the hydrostatic extrusion of tubes a tubular billet is inserted in a pressure chamber formed by a cylinder, a die with an opening to shape the product to the de-. sired outer cross section and a pressure-generating plunger which, when inserted into the cylinder generates the pressure required for the extrusion process in a pressure medium enclosed in the pressure chamber, the pressure medium surrounding the billet and operating on all sides of it. When extruding tubes a mandrel is used which cooperates with the die to form the hole through the tube. If the temperature of the billet is raised, a greater extrusion ratio can be obtained for a certain pressure.

When manufacturing copper tubing, a product is aimed at which is soft and free from oxide on the surface. It is particularly desirable to obtain an inner sur face which is free from oxide since the inner surface is the most difficult to clean. Copper hardens if it is subjected to mechanical machining. In methods used for tube production such cold machining usually results in hard material and the tubes must then be soft-annealed. This annealing must be performed in such a way that no oxides are formed, for example by performing the annealing in an inert atmosphere. Otherwise oxides formed must be removed after annealing. Internal layers of oxide are particularly difficult to remove in tubes having small inner diameters.

When copper tubing is manufactured by means of by drostatic extrusion, extremely vigorous machining takes place during the shaping process which results in the tube material being extremely hard when it leaves the die. However, by using the present invention it is possible to avoid the drawbacks mentioned above and soft, clean copper tubing is manufactured in a single ste 'l he deformation caused by hydrostatic extrusion also results in a considerable increase in temperature. At a pressure of kbar the adiabatic temperature increase is about 290C for copper. Experiments have shown that the temperature increase in the extruded product immediately after the die opening is of approximately the same magnitude as said theoretical adiabatic temperature increase.

SUMMARY OF THE INVENTION This temperature increase during the deformation is exploited in the method according to the invention. If a pre-heated billet is taken and extruded at a sufficiently high extrusion ratio, a temperature is reached which is above the value at which recrystallization is obtained which makes the copper in the extrudedtube soft. By cooling the extruded tube at such a distance from the die that the time between extrusion and cooling exceeds the recrystallization time required for softening copper at the temperature in question, a flexible material-is obtained inthe product immediately in connection with the extrusion process. In order to avoid oxidation of the copper tube, it is surrounded by an inert gas as far as a cooling zone. In practice, this is arranged so that the extmded copper tube is led to the cooling zone by a guide tube which is kept filled with inert gas. In order to obtain a product of the desired quality economically the tubular billet should be heated to above 250C, the extrusion ratio, by which is meant that the ratio between the cross section of the billet and that of the finished product exceeds 200:1 and the time between shaping in the die and cooling exceeds I second. An extremely uniform and high quality is obtained very economically if the billet is heated to about 350C, the extrusion pressure is between 10 and I5 kbar and there is a time of about 2 seconds between extrusion and cooling. Since the extrusion speed may be up to 15 m/sec, the distance between the die and the cooling zone must be about 30 in. Under the extrusion conditions described above, the temperature of the tube at the opening of the die is between 600 and 700C which means that recrystallization is substantially complete and the material has acquired its final hardness in less than 2 seconds. The time chosen be tween extrusion and cooling thus gives a high margin of safety. It may be practical to provide the end of the tube with a plug or lid which prevents the air coolant from penetrating into the tube.

The invention also relatesto extrusion equipment for performing the method. This includes a hydrostatic ex- .trusion press of a type known per se. To the outlet of the press is connected a guide tube through which the extruded copper tube is led to a cooling zone. This .guide tube is kept filled with an inert gas which is supplied to the tube from a gas source in connection with the tube. The gas source is suitably connected to the guide tube close to the press. The cooling zone is located at the outlet end of the guide tube and may include one or more cooling units built into the guide tube, in which units a coolant, usually water, is sprayed against the tube. Between the cooling units and the end of the guide tube there may be an outlet for the cooling water. This prevents the cooling water from spraying out through the opening of the guide tube into a reeling device for the extruded tube.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be further described with reference to the accompanying drawings;

FIG. 1 shows the relationship between hardness and time after copper which has acquired great hardness due to mechanical treating has been heated;

FIG. 2 shows aside view of the extrusion equipment;

FIG. 3 shows on a larger scale a side view of the lefthand part of the equipment;

FIG. 4 of its righthand part;

FIG. 5 a view from above of its lefthand part;

FIG. 6 a section through a cooling unit and FIG. 7 an outlet unit for coolant.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows in principle the ratio between; the hardness of the copper and the time when the hard copper is heated to different temperatures. In the drawings 1 designates an extrusion press, 2 a guide tube which is connected to the press and leads an extruded copper tube to a coiler 3 for coiling up the tube. The press 1 is of considerable length. It may have a guide tube which is more than 30 m in length. By placing the tube some meters above the floor surface, as shown in FIG. 1, the space under the guide tube can be used for other purposes. The lefthand end of the guide tube is connected to the outlet opening for the extruded product and is connected near the press to a gas container 4 containing inert gas by the conduit 5 having valves 6 and 7 to regulate the amount of gass to be supplied to the guide tube 2. Cooling units 10 are arranged in the righthand part of the guide tube. These comprise a housing 11 having flanges 12 which can be joined to flanges 13 on the guide tube 2. The housing 11 is provided with a number of connection sockets for tubes or nozzles for the supply of coolant. The coolant source is not shown. In the righthand part of the guide tube between the cooling units 10 and the outlet of the guide tube is a device 14 to drain off water, consisting of a housing 15 with a perforated or slotted tube 16 and flanges 18. This water drain 14 is also provided with a connection socket 19 so that the unit can be connected to a suction pump. By means of effective suction most of the coolant supplied can be removed so that only a small amount runs out through the outlet of the guide tube. This facilitates coiling of the extruded tube.

When copper is extruded the product will be extremely hard due to the vigorous machining caused by the area reduction. If a copper billet is extruded at such an extrusion ratio that the extrusion pressure is about 10 kbar, a temperature increase of about 300C is obtained. 1f the billet is heated to about 350C the extruded product will have a temperature of about 650C. At the die opening the copper product has a hardness of H (see FIG. 1). Because of the high temperature, 650C, a recrystallization occurs so that the hardness of the material decreases. By cooling the material at a suitable moment after the extrusion process it is possible to anneal the material in connection with the extrusion process. A period of 2 seconds between shaping in the die and cooling is sufficient under the extrusion conditions described above. The extrusion rate may be up to 15 m/sec which means that the cooling zone must be arranged at a distance of about m from the die. By leading the extruded copper tube through a closed tube filled with inert gas from the press to the cooling zone, oxidation of the hot tube both externally and internally is prevented. During its passage through the guide tube the front part of the extruded tube is filled with inert gas and, after leaving the guide tube, air may enter the copper tube. The inert gas remains in the inner part of the extruded copper tube in the form of a gas column so that air does notcome into contact with the hot inner tube surface between the press and the cooling zones. After the cooling zones the temperature is so low that contact with air does not cause any great inconvenience. However, it is possible to provide the extruded tube with a plug or lid which completely stops any air or cooling water from flowing in. The inert gas may be nitrogen, but any other gas which does not affect copper in a damaging manner under the conditions prevailing can be used. The cooling zone may comprise one or more cooling units by means of which cooling water is sprayed against the extruded copper tube. It is suitable to place one or more drainage devices 14 between the cooling units and the opening of the guide tube 2. If these drainage devices are connected to a powerful suction pump most of the coolant can be drained off. Water spraying is thus prevented on the coiling machine 3.

We claim:

1. Method for manufacturing copper tubes by means of hydrostatic extrusion, which comprises heating a tubular copper billet, inserting the heated billet in an extrusion press (1), extruding the heated billet through a gap between a die and a mandrel to form tubes having the desired cross-section under the influence of hydrostatic pressure, and leading the formed tube to a cooling zone at such a distance from the extrusion press that the time between shaping and cooling exceeds the recrystallization time required for annealing copper.

2. Method according to claim 1, which includes surrounding the extruded copper tube by an inert gas up to the cooling zone.

3. Method according to claim 1, which comprises leading the extruded copper tube to the cooling zone by a tube (2) which is kept filled with an inert gas.

4. Method according to claim 1, in which the tubular billet is heated to a temperature above 250C.

5. Method according to claim 1, in which the extrusion ratio exceeds 200:1.

6. Method according to claim 1, in which the time between shaping the tube and cooling exceeds 1 second.

7. Method according to claim 1, in which the billet is heated to about 350C, the extrusion ratio is about 500:1 and the time between shaping between die and mandrel and the cooling is about 2 seconds.

8. Method according to claim 1, which comprises providing the extruded tube with a member which seals the opening and prevents gas and coolant from penetrating into the tube. 

1. Method for manufacturing copper tubes by means of hydrostatic extrusion, which comprises heating a tubular copper billet, inserting the heated billet in an extrusion press (1), extruding the heated billet through a gap between a die and a mandrel to form tubes having the desired cross-section under the influence of hydrostatic pressure, and leading the formed tube to a cooling zone at such a diStance from the extrusion press that the time between shaping and cooling exceeds the recrystallization time required for annealing copper.
 2. Method according to claim 1, which includes surrounding the extruded copper tube by an inert gas up to the cooling zone.
 3. Method according to claim 1, which comprises leading the extruded copper tube to the cooling zone by a tube (2) which is kept filled with an inert gas.
 4. Method according to claim 1, in which the tubular billet is heated to a temperature above 250*C.
 5. Method according to claim 1, in which the extrusion ratio exceeds 200:1.
 6. Method according to claim 1, in which the time between shaping the tube and cooling exceeds 1 second.
 7. Method according to claim 1, in which the billet is heated to about 350*C, the extrusion ratio is about 500:1 and the time between shaping between die and mandrel and the cooling is about 2 seconds.
 8. Method according to claim 1, which comprises providing the extruded tube with a member which seals the opening and prevents gas and coolant from penetrating into the tube. 